Compressional wave sender or receiver



Nov. 29, 1938. w. KUNZE 2,138,036

COMPRESSIONAL WAVE SENDER OR RECEIVER I Filed Sept. 9, 1933 f 4 Ex wk; 9 FIG. I g z FIG. 3

| 'F; .10 g 4 l M 5 FIG. 4 3 4 l2 INVENTOR wi/ly ffunze UNITED STATES PATENT OFFICE COMPRESSIONAL WAVE SENDER OR RECEIVER Willy Kunze, Bremen, Germany, assignor to Submarine Signal Company, Boston, Mass., acorporation of Maine Application September 9, 1933, Serial No. 688,770 In Germany December 24, 1932 3 Claims. (Cl. 177-386) The present invention relates to underwater They are consequently very well adapted for sound receivers and transmitters and more parnoise reception. If they are to be used for sigticularly to such instruments employing piezonal reception, then care must be taken by suitelectric crystals. ably dimensioning the crystal with respect to the In the past the piezo-electric properties of cooperating metal elements that oscillatory sys- 5 quartz have been employed for sending and retems result whose natural frequency coincides ceiving sound waves in water. However, quartz with the signal frequency. instruments have had a number of disadvantages Rochelle-salt crystals are soluble in water. It which were particularly noticeable when used for is for this reason necessary to place them in a receiving. On the one hand, the piezo-electric watertight housing. The crystals are preferably 10 effect of quartz is comparatively weak so that cut to provide two surfaces which are perpendicgreat amplification had to be resorted to in orular to an electrical axis and to permit the comder to obtain the necessary results. On the othpressional wave vibrations to act upon the sur er hand, quartz is a comparatively expensive mafaces. The receivers can be so built that only terial which usually can be obtained in only relone surface is acted upon by the pressure waves 15 atively small crystals which, therefore, must be while the other surface of the crystal is rigidly assembled by special means in a mosaic fashion fastened to a fixed mass in the housing, or alto produce senders or receivers of reasonable ternatively both surfaces may be arranged to size. Practical results can only be obtained with be acted upon by the pressure waves in the waquartz if the natural resonance of the crystals is ter. 2

made use of. Further features of the invention will be ap- It has been known that substantially better parent from the description of the arrangement piezo-electric operation can be obtained with shown in the drawing in which Fig. 1 shows a certain other crystals, for example, of such salts double diaphragm transmitter or receiver and as sodium potassium tartrate which are also Fig. 2 shows a plan view looking at Fig. 1 from 25 known as Rochelle-salt crystals. Experiments the bottom; Fig. 3 shows in vertical section a have shown that the use of Rochelle-salt crysmodification of the device shown in Fig. 1; and tals is particularly advantageous for receiving Fig 4 is a horizontal section of the modification sound in water. shown in Fig. 3; Fig. 5 shows a further modifica- One object of the present invention is to protion in which a single thin rubber diaphragm is 30 vide for submarine sound senders and receivers used to conduct the vibrations to and from the a means for utilizing the piezo-electric effect of crystals and the water.

Rochelle-salt crystals for the transformation of A simple construction of a Rochelle-salt sender compressional vibrations into electric vibrations, or receiver is shown in Fig. 5 in which the radiatand vice versa. Rochelle-salt crystals can reading surface of the crystal is covered with a thin 35 ily be produced in comparatively large sizes and rubber diaphragm which protects the crystal are relatively cheap. Their special value lies, chamber from the water. A rather massive pothowever, in the fact that as compared with the shaped metallic housing I contains the crystal piezo-electric materials which have been used 2 which is mounted so that one surface 3 is rigin the past Rochelle-salt crystals produce espeidly held against the back wall of the housing 40 cially energetic effects. which is in the form of a rigid mass. The other The conditions attending sound transmission surface 4 projects slightly from the opening of under water are not accompanied by comparathe housing. The surface 4 is covered by a diatively large amplitudes of the medium with relphragm 5, for example, of rubber whose outer atively small pressure changes as is the case in edge is tightly clamped to the housing by a 45 air, but vice versa with'large pressure changes clamping ring 6. Care is taken that there is and small amplitudes. For this reason a Rosubstantially no space between the crystal and chelle-salt crystal is particularly advantageous the walls of the housing in which a pressure re since it responds well to pressure variations, and lease could take place. Two metal plates 1, for

it is especially good for underwater sound reexample, in the form of leaf springs, press light- 50 ceivers. Since these crystals have no natural ly against the crystal and act as electrodes. They frequency in the audio frequency range, it is posare fastened to the housing by means of insulatsible by means of these crystals to build submaringmembers 8. Two conductors 9 and I0 lead ine sound receivers which can receive over the out of the housing and connect with cable ll.

entire audible frequency range without distortion. Sound waves in water striking the rubber dia- 55 phragm 5 are transferred to the crystal 2 and by virtue of the piezo-electric efiect produce corresponding electrical potential variations at the electrodes 7, which are conducted to an amplifier and made audible in this manner.

If the two conductors are connected to the terminals of an alternating current source, the

receiver may be used as a sender. To increase the piezo-electric effect while receiving it may be desirable to apply to the electrodes a polarizing potential. It should be noted, however, that the diaphragm 5 produces in itself a definite constant initial pressure upon the crystal, thereby giving it a pressure polarization.

If the surface covered by the crystal is sufficiently large, one obtains a sharp directional effect, that is to say, when the wave length of the sound is small with respect to the dimensions of the diaphragm.

A double-diaphragm instrument is shown in Figs. 1 and 2. In these figures I is a rigid housing closed at one end by a piston diaphragm 2 forming part of the housing and closed at the other end by a cover I which also forms the piston diaphragm 3. Between the piston diaphragms is mounted the Rochelle-salt crystal 5. 6 and I are electrodes, for example, thin metal foil mounted on the crystal by suitable adhesive and connected to the conductors 8 and 9 which serve to conduct electric energy to and from the crystals. The inner surfaces of the piston diaphragms 2 and 3 are separated from the crystal by insulating layers I and are pressed tightly against the crystal by the tension of the diaphragms.

It will be noted that the areas of the diaphragms are large compared with the areas of the active surfaces of the crystal. This has the effect of greatly increasing the sensitivity of the device when used as a receiver.

The increased sensitivity by virtue of the larger radiating surface can also be obtained by means of the modification shown in Figs. 3 and 4. In this case the radiating surfaces are semicylindrical in form. In Figs. 3 and 4 the Rochelle-salt crystal 5 is mounted between two semi-cylindricalrigid bodies II. On the other hand, the members II may be made of insulating material. The members are held together by a shell I2 which may be of rubber and designed to press the members II tightly against the surfaces of the crystal 5. I3 and I I are two metal plates which serve as holding members for the shell I2 which is clamped to them by means of the rings I! and I8 which press the shell I2 into grooves I5 and IS in the members I3 and I4. The whole arrangement is in this manner made watertight.

It will be observed that the curved surfaces of the members II serve as radiating surfaces while the internal surfaces of the members II are made fiat and are pressed against the crystal. In order that the members II may each vibrate as nearly as possible as a whole and transfer the pressure with best efllciency to the crystal 5, they are separated by a small air space. However, the use of the shell I2, as shown in Figs. 3 and 4, is thought to be preferable and avoids the necessity of filling the spaces between the members II, so that they can vibrate freely.

In the devices according to the present invention care should be taken to avoid any looseness between the diaphragm and the crystal or between the crystal and the back plate in order that the pressure variations may be efliciently transferred to the crystal. To this end the crystal may be mounted on the housing or the diaphragm by a suitable adhesive or by other suitable means.

It has been found that with the described devices distortionless reception with sumcient sensitivity may be obtained up to 20,000 cycles per second. The devices are therefore particularly useful for the receipt of frequencies in the vicinity of or above the audible range. They are also useful for noise reception on account of their large frequency range. Whenever it is necessary that the received sound vibrations be transformed into electrical vibrations with as nearly the same phase relations as possible as is, for example, the case with group of the so-called multispot listening arrangements, the receivers according to the present invention are particularly advantageous.

Also when used in a device towed by a moving vessel, for example, in which a plurality of receivers are arranged in a straight line at equal distances from one another, the receiver according to the present invention is of particular advantage on account of its freedom from disturbing noises. In this case the individual receivers are preferably enclosed within a common shell as, for example, a rubber housing which protects the receivers from the water and holds them at the proper distances from one another.

It will be understood that the present invention may be used for producing sound waves in water by applying a potential to the electrodes.

Having now described my invention, I claim:

1. A compressional wave submarine sender or receiver comprising a. housing closed at one end by a heavy mass and having an opening at the other end, a Rochelle-salt piezo-electric crystal, having electric and compressional axes, mounted therein in contact with said mass and with its compressional axis perpendicular to the plane of said opening, a yielding rubber-like diaphragm in contact with said crystal and covering said opening, said diaphragm having a thin portion between the place of contact of the crystal and the edge of the opening, and means for conducting electric energy to or from the electric axes of said crystal.

2. A compressional wave submarine sender or receiver comprising a. housing closed at one end by a heavy mass and open at the other end, a Rochelle-salt piezo-electric crystal having electric and compressional axes mounted so that one compressional surface abuts said end mass and its opposite surface projects slightly through said opening, a rubber sheet, means for stretching said sheet over said opening and said projecting crystal surface, whereby the crystal is pressed firmly means for conducting electric energy to and from said crystal.

3. A compressional wave submarine sender or receiver comprising a casing having a heavy back wall and heavy sides and open at one end, a Rochelle-salt piezoelectric crystal substantially filling the interior of the casing and supported against the back thereof, said crystal having its compressional axes normal to the casing and extending substantially to the end surfaces of the sides thereof, a thin yielding diaphragm covering the open end of said casing and means clamping said diaphragm in position, said clamping means extending substantially to the edges of the inner wall of said opening.

WILLY KUNZE.

against the end mass of the housing, and 

